Influencing Factors of Heat Transfer Coefficient in Air and Gas Quenching

Cooling rates of work pieces in heat treating processes heavily depend on the interfacial heat transfer coefficient (HTC) between work pieces and quenchants. Because the HTC plays an important role in the resulted distortion, residual stress, and mechanical property distributions, understanding how the HTC varies with respect to various influencing factors is of importance for an optimal quenching process. In this paper, the influencing factors such as air/gas velocity, pressure, temperature, gas mixture and part orientation, air/gas temperature, air humidity, surface roughness, oxide, and material to the variation of HTC are studied experimentally by using the Center for Heat Treating Excellence quenching system and theoretically by using empirical equations.